Staphylococci includes 40 or more bacterium types roughly classified into Staphylococcus aureus and coagulase-negative staphylococci (hereafter abbreviated to “CNS”) from the clinical point of view. Staphylococcus aureus are regarded as pathogenic organisms and CNS are regarded as nonpathogenic organisms.
Infections are treated with the use of antibiotics. Since many staphylococci are drug-resistant, they are classified based on drug resistance from the clinical point of view.
Among Staphylococcus aureus that are clinically important pathogenic organisms, methicillin-resistant Staphylococcus aureus (MRSA) are Staphylococcus aureus that show resistance to β-lactam agents, including penicillin such as methicillin. Also, many such bacteria show resistance to many drugs such as aminoglycosides and macrolides. Thus, such bacteria are clinically regarded as multidrug-resistant Staphylococcus aureus. In contrast, Staphylococcus aureus showing sensitivity to methicillin are referred to as methcillin-sensitive Staphylococcus aureus (hereafter referred to as “MSSA”).
Staphylococcus aureus produce a variety of toxins, including enterotoxin, toxic-shock syndrome toxin, hemolysin, and exfoliative toxin (Hideo IGARASHI: TSST-1, “Shinshu to meneki (Invasion and immunity),” 3, 3-10, 1994). Infection with such toxins would cause enteritis, pneumonia, dermatitis, organic failure, or the like, and serious infection may lead to death. When Staphylococcus aureus are isolated from a patient, accordingly, whether or not the bacterium is MRSA must be inspected as quickly as possible. In the event of MRSA infections, adequate drugs, such as vancomycin or arbekacin sulfate, which are regarded as being effective against MRSA, must be selected and administered to a patient.
Staphylococci other than Staphylococcus aureus are indigenous bacteria, and they are nonpathogenic to healthy individuals in general. When an organ transplant patient takes an immunosuppressant as a measure to prevent a postoperative infection or in the case of a so-called compromised patient with a weakened immune system due to an aging-induced weakened physical strength, however, opportunistic infections may occur.
Some staphylococci other than Staphylococcus aureus have acquired methicillin resistance or multidrug resistance, and these bacteria are collectively referred to as methicillin-resistant coagulase-negative staphylococci (hereafter abbreviated as “MRCNS”) or multidrug-resistant coagulase-negative staphylococci, respectively. As with the case of MRSA, drugs that are effective against MRCNS are limited if a compromised patient is infected therewith. Thus, MRCNS has been a medical problem.
MRSA and MRCNS are collectively referred to as multidrug-resistant staphylococcus. 
The drug resistance of MRSA or MRCNS is known to result from expression of a new enzyme, PBP2′, in addition to four types of penicillin-binding proteins (i.e., PBP1, PBP2, PBP3, and PBP4) that crosslink murein chains, which are constitutional elements of the cell wall of staphylococci and which synthesize the cell wall (Utsui, Y., and Yokota, T.: Role of an altered penicillin-binding protein in methicillin- and cephem-resistant Staphyloccus aureus., Antimicrobial Agents and Chemotherapy, 28, 397-403, 1985). PBP1 to PBP4 proteins that staphylococci possess in common are inactivated as cell-wall-synthesizing enzymes by penicillin antibiotics, which are substrate analogues, and bacteria eventually die when synthesis of cell walls becomes unfeasible. However, MRSA and MRCNS express a new cell-wall-synthesizing enzyme, PBP2′, which exhibits little affinity to β-lactam antibiotic substances, i.e., which would not be inactivated thereby. MRSA and MRCNS are considered to proliferate by altering roles in cell wall synthesis. Most MRSA and MRCNS acquire mechanisms of resistance to other antibiotics and become multidrug-resistant bacteria that are resistant to many antibiotics. Such bacteria are regarded as multidrug-resistant staphylococci instead of staphylococci having resistance merely to β-lactam antibiotics.
General techniques for separating and identifying staphylococci involve the use of nasal cavity swabs, pharyngeal swabs, sputum, blood, pus, stool, or other samples as clinical samples, and isolation culture thereof with the use of an agar medium or liquid agar medium is performed. When cultured in an agar medium, colonies suspected of being staphylococci are selected from among the grown colonies and further subjected to pure culture, and staphylococci or Staphylococcus aureus are identified via microscopic visualization of Gram-stained images or biochemical character tests of coagulase production capacity or mannitol degradation capacity. When cultured in a liquid medium, a culture solution is sowed on an agar medium and cultured therein for colony isolation, and colonies suspected of being staphylococci are also subjected to pure culture followed by identification. The bacteria that have been identified as the Staphylococcus aureus or staphylococci are subjected to a drug-sensitivity test or the like, and whether or not a bacterium of interest is MRSA, MSSA, or MRCNS is determined based on test results. A drug-sensitivity test is generally carried out by culture, such as a dilution technique or a disk sensitivity test. Such drug sensitivity test is known to require a culture duration of 16 to 24 hours (it would take 3 or more days from separation of clinical samples to determination if both isolation culture and pure culture are conducted) and to produce differences in test results due to, for example, the concentration of bacteria, culture temperature, medium composition, or drug to be used. Thus, a person who conducts such test is required to be highly experienced with the procedure.
In recent years, a method that detects the mecA gene encoding PBP2′, which is a main body of a drug-resistant mechanism, via pure culture, isolation culture, or directly from a clinical sample via PCR to evaluate antibody resistance based on the conditions of the mecA gene carried in the analyte bacterium has been developed. However, the fact that a bacterium carries the mecA gene does not always mean the expression of antibiotic resistance, and some bacteria have not acquired resistance even though they carry such gene.
As described above, production of PBP2′ plays a key role in the expression of multidrug resistance, and detection of PBP2′ from staphylococci can be a useful means for learning whether or not a bacterium of interest has acquired resistance.
PBP2′ produced specifically by bacteria of the multidrug-resistant staphylococcus, including MRSA, is detected by an antigen-antibody-reaction-based immunological means, such as Western blotting, radioimmunoassay, or a slide latex agglutination test (JP Patent No. 3638731). Such methods of detecting PBP2′, however, suffer from the following problems. Western blotting is complicated in terms of procedure, and it is difficult to rapidly process many samples. Radioimmunoassay is not practical from the viewpoint of routine testing, since it involves the use of a radioisotope, it requires BF separation involving separating an antigen-antibody complex from other non-binding antigens or antibodies during assay, and it requires several hours to complete assay due to the presence of a denaturing agent used for extracting an antigen from the bacterium in the reaction system. The slide latex agglutination test requires detection from axenic bacteria due to false-positive reactions caused by contaminating bacteria (e.g., false-positive reactions due to nonspecific reactions) and low sensitivity. Thus, culture must be conducted at least twice, i.e., isolation culture and pure culture, which in turn requires 2 to 3 days to complete the determination, it increases the cost for mediums for pure culture, and it may cause a false-positive reaction due to agglutination after the determination time, even though such time can be as short as 3 minutes. It is also laborious due to the need of centrifugation for separating a PBP2′-containing supernatant from cell-wall-derived pieces at the time of pretreatment of extracting PBP2′ from the bacterium, which may contaminate the environment of the laboratory, it involves complicated procedures such as transfer of a supernatant after centrifugation via pipetting, and it involves boiling. Accordingly, a method that can rapidly detect PBP2′ produced specifically by a bacterium of multidrug-resistant staphylococcus with high specificity and sensitivity has been awaited as a replacement for conventional detection techniques.